The fermentation industry consumes very large quantities of feedstock materials each year. Successful commercial fermentation depends on designing fermentation media containing nutrient sources optimal for microbial growth and product formation. Bioprocess nutrients include sources of carbon, nitrogen, inorganic components, and vitamins. Often complex "natural" sources of nitrogen are chosen which supply not only nitrogen, but also carbohydrate, vitamins, minerals, and other microbial growth factors. Commonly used materials include soybean meal or flour, fish meal, and corn steep liquor. All of these crude naturally derived products have the advantage of being relatively inexpensive compared to complex specialty medium ingredients, such as yeast extracts or highly processed oilseed meals.
Since the crude naturally derived products were not designed for fermentation applications, potential drawbacks to their effectiveness exist. For example, these crude materials contain very little readily-available nitrogen. This limits their use as nitrogen sources in fermentation by microorganisms which do not excrete extracellular proteases, and by microbes that require some readily-available nitrogen for growth in the early stages of fermentation prior to effectively utilizing protein. A common measure of the readily available nitrogen in a nutrient is the amount of free amino nitrogen ("FAN content") of the material. Crude naturally derived materials can also contain significant amounts of insoluble, unusable materials which must be separated from the product of interest and disposed of after fermentation. Finally, since these crude feedstock materials are products of the agricultural and food processing industries, their consistency and/or quality can be variable.
To be an effective nitrogen source in fermentation, protein must generally first be hydrolyzed to its constituent small peptides and individual amino acids. This can be accomplished either during fermentation by proteolytic enzymes excreted by the fermenting microorganism, or provided directly in a pre-digested form as a fermentation medium ingredient. Protein nitrogen in this more bioavailable form is known as free amino nitrogen ("FAN"). FAN is a measure of the quantity of amino nitrogen available during fermentation, and refers specifically to the amount of small peptides, amino acids, and ammonia. Commercial products employed to provide higher FAN in fermentation media include yeast extracts and protein hydrolysates. Potential substrates for hydrolysis include casein or sunflower, rapeseed, soy, meat, and bone meals, and the starting material for the hydrolysis ultimately dictates the composition of the final product.
To supply nitrogen needs in fermentation media, soybean meal and flours are often used in combination with more expensive yeast extracts or soy isolates/concentrates. This combination provides both "readily-available" nitrogen and "slow-release" protein for the duration of the fermentation. The need to supplement crude protein feedstocks with more expensive defined nutrient sources, however, can greatly increase raw material costs.
The latent nutritional values present in many vegetables, particularly the oilseed vegetables such as soybeans and other legumes and cottonseeds, is well known. Utilization of these nutrient sources has been severely hampered, however, by the presence in these vegetable nutrients of naturally occurring substances that can interfere with the growth of organisms. The principal deficiencies of vegetable nutrient sources for use in fermentation media (in addition to low FAN content) are the presence of antinutritional factors such as trypsin inhibitor, lectins and phytic acid. While some of these factors may be reduced to lower levels by heat treatment, such heat treatments are not always effective or desirable.